# Explain why the incomplete combustion of hydrocarbon fuels in car engines is considered harmful to human health and the environment.

> Cambridge International IGCSE Chemistry (0620) — 11.3 Fuels · Explain · 4 marks

> Car engines burn petrol, a mixture of hydrocarbons. When the supply of air to the engine is limited, the combustion of petrol is incomplete.

## Mark scheme (4 marks)

1. Incomplete combustion produces carbon monoxide
2. Carbon monoxide is toxic / poisonous to humans
3. Incomplete combustion produces carbon particles / soot
4. Carbon particles / soot cause respiratory problems OR contribute to global dimming / reduced sunlight

## Key terms

- [incomplete combustion](https://www.gradenine.co.uk/glossary/incomplete-combustion)
- [hydrocarbon](https://www.gradenine.co.uk/glossary/hydrocarbon)

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-incomplete-combustion-of-28c1fbe7) · Published by Druglandscape Ltd.